Add constraints programmatically

Above iOS6, AutoLayout is coming.
My current team uses programmatically UI style to realize complicated UI.
We can set constraint in xib and storyboard by UI.
But, in case of programmatically, what should we do?

Steps

Create UI set with NSDictionaryOfVariableBindings
Create constraints using constraintsWithVisualFormat.
This example I used,
H:|-10-[_button1(44)]-10-|
Horizontal, make space 10px at the left side, button1 size(width) is 44px, make space 10px at the right side.
V:|-10-[_button1(44)]
Vertical, make space 10px at the top, button1 size(height) is 44px

constraintsWithVisualFormat is to create constraint format.
Details of the format is in reference pages(next topic).

In this case, I implemented in viewDidLoad.
Actually, this topic is a bit difficult.
I still go on research.